Network for generating a CRT control signal for enhancing the edges of television images

Abstract

A low cost network for use in a television receiver for receiving a video signal and generating therefrom both a control signal for modulating the scan velocity of a CRT electron beam and a delayed video signal for intensity modulating the CRT electron beam with picture information. The network uses only one delay line for generating the control signal and the delayed video signal. A video signal is applied to an impedance means followed by a delay means coupled to a reflecting termination. The impedance of the impedance means is substantially equal to the characteristic impedance of the delay means. An output terminal from which the control signal is taken is included at a point between the impedance means and the delay means. The delayed video signal is generated by means responsive to the signal received by the reflecting termination from the delay means. The network may also be used to generate preshoot and overshoot peaking components for peaking the delayed video signal.

I claim: 
     
       1. In a television receiver, a network for receiving a video signal and generating therefrom both a delayed video signal for intensity modulating a CRT electron beam with picture information and a control signal for modulating the scan velocity of the CRT electron beam so as to enhance the sharpness of the television image, said network comprising, in cascade: impedance means having an input port and an output port;   delay means having an input port and an output port with its input port coupled to the output port of said impedance means, the impedance means having an impedance at its output port which is substantially equal to the characteristic impedance of the delay means;   a reflecting termination coupled to the output port of said delay means, which termination is reflective of signals received from said delay means and in the frequency range of the video signal;   means for applying the video signal to the input port of said impedance means;   an output terminal at a point between said impedance means and said delay means from which the control signal is taken; and   means responsive to the signal received by the reflecting termination from said delay means for generating a signal for use as the delayed video signal which is substantially proportional to the signal received by the reflecting termination.   
     
     
       2. A network as set forth in claim 1 which includes means responsive to the current in the output port of said impedance means and to the signal received by the reflecting termination from said delay means for generating first and second currents which are proportional to the current in the output port of said impedance means and to the signal received by the reflecting termination, respectively, and for matrixing said first and second currents to generate preshoot and overshoot peaking components for peaking the delayed video signal. 
     
     
       3. A network as set forth in claim 1 wherein the delay associated with said delay means is substantially equal to one half the period of 3.58 MHz color subcarrier signal so as to cause the control signal appearing at said output terminal to be substantially free of 3.58 MHz signal components. 
     
     
       4. In a system for enhancing the sharpness of television images on a CRT, a network for receiving a video signal and generating therefrom a control signal for modulating the scan velocity of the CRT electron beam, a delayed video signal for intensity modulating the CRT electron beam with picture information, and preshoot and overshoot peaking components for peaking the delayed video signal so as to further enhance the sharpness of the television image, said network comprising: impedance means having an input port and an output port;   delay means having an input port and an output port with its input port coupled to the output port of said impedance means, the impedance means having an impedance at its output port which is substantially equal to the characteristic impedance of the delay means;   a reflecting termination coupled to the output port of said delay means, which termination is reflective of signals received from said delay means and in the frequency range of the video signal;   means for applying the video signal to the input port of said impedance means;   an output terminal at a point between said impedance means and said delay means from which the control signal is taken;   means responsive to the current in the output port of said impedance means for generating a current I 1  proportional thereto;   means responsive to the signal received by the reflecting termination for generating a current I 2  proportional thereto;   means receiving the current I 2  for generating a voltage which is proportional to I 2  for use as said delayed video signal; and   means receiving the currents I 1  and I 2  for generating a peaking signal proportional to (I 1  -I 2 ), said peaking signal consisting of preshoot and overshoot peaking components for application to and peaking of the delayed video signal.   
     
     
       5. In a system for enhancing the sharpness of television images on a CRT, a network for receiving a video signal and generating therefrom a control signal for modulating the scan velocity of the CRT electron beam, a delayed video signal for intensity modulating a CRT electron beam with picture information, and preshoot and overshoot peaking components for peaking the delayed video signal so as to further enhance the sharpness of the television image, said network comprising: a first transistor having a base terminal, an emitter terminal and a collector terminal, with the base terminal receiving said video signal;   a first collector circuit branch coupled to the collector terminal of said first transistor, through which the collector current, I 1 , of said first transistor flows;   impedance means coupled to the emitter terminal of said first transistor;   a delay line having an input terminal and an output terminal, with its input terminal serially coupled to said impedance means, the impedance means having an impedance equal to the characteristic impedance of the delay line;   a second transistor having a base terminal, a collector terminal and an emitter terminal, with the emitter terminal serially coupled to the output terminal of said delay line;   an output terminal at a point between the impedance means and the delay line from which the control signal is taken;   a resistance element connected between the emitter terminal of said second transistor and a reference voltage level;   a second collector circuit branch coupled to the collector terminal of said second transistor, through which the collector current, I 2 , of said second transistor flows, said second collector circuit branch including a substantially linear resistance element serially coupled to the collector terminal of said second transistor and across which is developed a voltage for use as said delayed video signal; and   means coupled to said first and second collector circuit branches for matrixing the currents I 1  and I 2  to develop a peaking signal proportional to (I 1  -I 2 ), said peaking signal consisting of preshoot and overshoot peaking components for application to and peaking of the delayed video signal.